Mean Size Distribution Research Articles

Particle optical properties at a Central Mediterranean site: Impact of advection routes and local meteorology

A multiwavelength integrating nephelometer and a PM10 sampler have been used to continuously measure optical properties and mass concentrations of particles at the ground level with the main aim of determining airflow and local meteorology effects on particle optical properties and PM10 mass concentrations. Measurements have been performed at Lecce (Italy), a coastal site in the Central Mediterranean and included scattering (σp) and hemispheric backscattering (βp) coefficients, and hemispheric backscattering fraction (βp/σp) at three wavelengths (450, 525, and 635nm), in addition to PM10 concentrations. The scattering Ångström exponent (å (λ1, λ2)) for different wavelength pairs (λ1, λ2), and the scattering Ångström exponent difference (∆å=å (450nm, 525nm)−å (525nm, 635nm)) have been calculated to estimate the airflow impact on the relative weight of fine and coarse mode particles. The yearly mean values±1 standard deviation of σp (450nm), βp (450nm), βp/σp (450nm), å (450, 635nm) and ∆å are equal to 100±50Mm−1, 12±6Mm−1, 0.13±0.02, 1.1±0.4, and 0.2±0.2, respectively. σp is well correlated to PM10 mass concentrations (r=0.96) and the PM10 mass scattering cross section is equal to 3.6±0.1m2g−1. The back trajectory cluster analysis has identified 5, 5, 7 and 7 distinct airflow types reaching the study site at 271, 500, 1500 and 3000m above the sea level, respectively, with only slight differences in airflow type among the four arrival heights. We have found that σp and βp values and their respective dependence on wavelength are strongly dependent on airflows. Therefore, we have shown that the in situ particle properties and the local meteorological parameters vary with advection routes. Given the dependence of å, ∆å, and βp/σp on particle size and shape, their strong association with airflows has indicated that the mean size distribution of sampled particles varies with air mass history and it has been shown that å, ∆å, and βp/σp values allow a satisfactory differentiation of the particle properties associated with different advection routes. More specifically, å and ∆å values have allowed distinguishing the airflows mainly responsible for the advection of fine mode particles from the ones which are mainly responsible for the advection of coarse mode particles. These results have provided a satisfactory understanding of the dependence on air flows of the mass scattering cross section values which vary from 2.9±0.2m2g−1 to 4.3±0.1m2g−1 with air flows. The airflow analysis has also allowed understanding the seasonality of the particle optical properties being linked to the airflow seasonality.

ChemInform Abstract: Kinetics and Mechanisms of Aggregative Nanocrystal Growth

AbstractReview: 206 refs.

Evolution of electrochemical interfaces in solid oxide fuel cells (SOFC): a Ni and Zr resonant anomalous ultra-small-angle X-ray scattering study with elemental and spatial resolution across the cell assembly

Electrochemical interfaces are key to the direct conversion of fuels to electrical energy and lend energy converters like solid oxide fuel cells (SOFC) their functionality. Over extended operation at high temperatures, the microstructure of the underlying component materials in the cathodes, anodes and electrolytes evolve to an extent that these interfaces become affected and ultimately impaired, giving rise to performance degradation. We present anomalous ultra-small-angle X-ray scattering (anomalous USAXS) measurements to quantify the component phase interfacial surface areas as a function of position within the electrodes and electrolyte of a SOFC assembly. Using USAXS at a 3rd generation X-ray synchrotron facility, the primary microstructural parameters obtained are the mean feature size, size distribution and surface area, determined over a contiguous length scale from nanometers to micrometers in a single measurement at a given position. Here, a spatial resolution of <20 μm has been achieved perpendicular to the SOFC electrode and electrolyte layers. Anomalous USAXS measurements at X-ray energies just below the Ni and Zr K-absorption edges have enabled the electrochemically-active solid components and their associated void morphologies to be distinguished from each other close to the electrode/electrolyte interfaces. The anomalous variation of the X-ray scattering contrast with X-ray energy has been exploited to distinguish Ni-rich or Zr-rich component microstructures from adjacent phases, and to determine the interfacial surface areas both between specific solid phases and between each phase and the void network. Such information provides improved insights for relating the morphology of the SOFC triple phase boundary (TPB, where the reactant gas, electron-conducting and ion-conducting phases coincide) to the various component interfaces in the adjacent microstructure. We demonstrate how such measurements determine the electrochemically-active interface response to SOFC service life, especially in the anode with and without sulfur present in the fuel. Our approach can be generalized to address degradation issues at a quantitative level in other electrochemical systems such as batteries and photo-electrochemical cells.

THEORETICAL AND EXPERIMENTAL PACKING DENSITY STUDY OF HYDROXYL TERMINATED POLYBUTADIENE-AMMONIUM PERCHLORATE BASED PROPELLANT AND ITS INFLUENCE ON BURNING RATE

A model that gives the particulate composition with maximum packing density and minimum viscosity for highly loaded trimodal hydroxyl terminated polybutadiene-ammonium perchlorate (HTPB-AP) based composite propellant was developed by using the packing density concept. The theoretical model developed by Furnas was utilized to predict particulate composition for maximum packing density. The apparent density of each component of trimodal propellant was determined by tapped density analyzer. The void fractions of the components were calculated from the apparent volumes of the component sizes and pre-known particle densities. Using the void fractions of AP components, the optimum size distribution was gathered by Furnas' method. Least-squares technique was used to test the closeness to the optimum size distribution. The fractions of solid components were calculated for the maximum packing and minimum viscosity. The model was tested by rheological characterization of uncured propellant with the predetermined fractions of components. The variation of viscosity with overall void fraction of the propellant was obtained. For trimodal concentrated suspension of two propellants containing the same mean particle size and size distribution of AP particles from different suppliers, different mix viscosity values were obtained due to different shape and surface characteristics of particles shown by scanning electron microscopy analysis. The effect of both packing density and viscosity on the burning rate of propellant was also explored. It was realized that not only average particle size, but also void fraction of AP particles, were important parameters affecting burning rate and better packing changed ballistic properties of propellant.

Direct observation of aggregative nanoparticle growth: kinetic modeling of the size distribution and growth rate.

Direct observations of solution-phase nanoparticle growth using in situ liquid transmission electron microscopy (TEM) have demonstrated the importance of "non-classical" growth mechanisms, such as aggregation and coalescence, on the growth and final morphology of nanocrystals at the atomic and single nanoparticle scales. To date, groups have quantitatively interpreted the mean growth rate of nanoparticles in terms of the Lifshitz-Slyozov-Wagner (LSW) model for Ostwald ripening, but less attention has been paid to modeling the corresponding particle size distribution. Here we use in situ fluid stage scanning TEM to demonstrate that silver nanoparticles grow by a length-scale dependent mechanism, where individual nanoparticles grow by monomer attachment but ensemble-scale growth is dominated by aggregation. Although our observed mean nanoparticle growth rate is consistent with the LSW model, we show that the corresponding particle size distribution is broader and more symmetric than predicted by LSW. Following direct observations of aggregation, we interpret the ensemble-scale growth using Smoluchowski kinetics and demonstrate that the Smoluchowski model quantitatively captures the mean growth rate and particle size distribution.

Intrinsic Focusing of the Particle Size Distribution in Colloids Containing Nanocrystals of Two Different Crystal Phases

We have studied the Ostwald ripening of colloids containing nanocrystals of two different crystal phases of the same material. Ostwald ripening in such polymorphic systems is shown to result in an intrinsic focusing of the particle size distribution of the thermodynamically preferred phase while the particles of the less stable phase completely dissolve. Experimentally, a colloidal system of this kind was realized by mixing small NaEuF4 nanocrystals of the cubic α-phase with particles of the hexagonal β-phase having the same mean size and size distribution. The temporal evolution of the particle sizes of both phases can be understood and numerically simulated within the framework of LSW theory. The simulations show that small differences in the bulk solubility or the surface energy of the two phases are sufficient to explain the experimentally observed narrowing of the particle size distribution.

Coefficient Estimation for 2D-Spline Equation, In Order to Correlate the Supercritical Rapid Expansion Process Data Points

Coefficients determination technique has been discussed for a 2D-Spline function correlating the experimental results of a rapid expansion process. The experimental phase was accomplished in order to achieve Ibuprofen nano-particles formation as a pre-requisite of a drug delivery system. The operational values were the mean size distribution of the processed Ibuprofen nano-particles in various extraction pressures and expansion device temperatures. Two 1D splines were developed separately along with each variable direction. A 2D-structured equation system was finally formulated through combining the 1D splines, and resolved expediently by arranging as a linear equation system. A Matlab encoding was carried out in order to estimate and optimize the equation system coefficient.

Nanosuspension improves tretinoin photostability and delivery to the skin

The aims of this work were to improve cutaneous targeting and photostability of tretinoin by using nanosuspension formulation. Tretinoin is a drug widely used in the topical treatment of various dermatological diseases. The tretinoin nanosuspension was prepared by precipitation method and then characterized by photo correlation spectroscopy for mean size and size distribution, and by transmission electron microscopy for morphological studies. An oil in water tretinoin nanoemulsion was also prepared and used as a control. Dermal and transdermal delivery of both tretinoin nanosuspension and nanoemulsion were tested in vitro by using Franz diffusion cells and newborn pig skin. Photodegradation studies were carried out by UV irradiation (1h, λ=366 nm) of the tretinoin nanosuspension in comparison with the nanoemulsion and a methanolic solution of the drug. During 8h percutaneous experiments, the nanosuspesion was able to localize the drug into the pig skin with a very low transdermal drug delivery, whereas the nanoemulsion greatly improved drug permeation. UV irradiation of the nanosuspension showed a great improvement of tretinoin stability in comparison with both controls. Overall results show that nanosuspension might be a useful formulation for improving tretinoin dermal delivery and stability.

Kinetics and Mechanisms of Aggregative Nanocrystal Growth

The aggregative growth and oriented attachment of nanocrystals and nanoparticles are reviewed, and they are contrasted to classical LaMer nucleation and growth, and to Ostwald ripening. Kinetic and mechanistic models are presented, and experiments directly observing aggregative growth and oriented attachment are summarized. Aggregative growth is described as a nonclassical nucleation and growth process. The concept of a nucleation function is introduced, and approximated with a Gaussian form. The height (Γmax) and width (Δtn) of the nucleation function are systematically varied by conditions that influence the colloidal stability of the small, primary nanocrystals participating in aggregative growth. The nucleation parameters Γmax and Δtn correlate with the final nanocrystal mean size and size distribution, affording a potential means of achieving nucleation control in nanocrystal synthesis.

Experimental Studies on the Effects of Process Parameters on Granule Properties in a Conical High Shear Granulator

Experimental work was carried out to investigate the influence of impeller speed, granulation time, binder mass and their interactions on granule size distribution, mean size and binder content distribution in a conical high shear granulator. It was observed that the response of high shear granulation to changes in process parameters varies significantly from one operating condition to another. For all quantities of binder, the granule mean size increased with time at lower impeller speeds, while the opposite trend was observed at higher impeller velocities. For long mixing times, increasing impeller speed decreased the granule average size constantly; whereas for other durations, an increase in the mean size followed by a decrease was observed across ascending impeller speeds. It was also found out that variations of the span of granule size distribution can be utilized to indicate the dominant rate process. Coalescence which was prevailing at lower impeller speeds, was limited by attrition, breakage or shattering at higher impeller velocities. Binder-solid ratio of granules showed a continuous increase across size at lower impeller speeds and a maximum at middle size range for higher impeller velocities. Binder content distribution showed different trends with time at different operating conditions. Furthermore, increasing impeller speed limited the domain of binder content variations and made the granule binder-solid ratio to be much closer to theoretical value.

Deterioration Behavior of Pt in a Pt/Au Nanoparticle-Loaded Carbon Black Catalyst Analyzed by an Accelerated Durability Test

Au nanoparticles with 2.5 ± 0.5 nm in size were prepared on carbon black by bubbling CO as a reducing agent in a KAuCl4 aqueous solution containing glutathione as a stabilizer (Au-G/CB). The Au nanoparticles after heat treatment (Au-G/CB-HT) had the mean particle size and size distribution of 2.8 ± 0.5 nm. Pt monolayer was deposited on the Au nanoparticles by underpotential deposition and the following galvanic replacement (Pt/Au-G/CB-HT). The activity per unit mass of Pt for oxygen reduction reaction for the Pt/Au-G/CB-HT at 0.9 V was ca. 6 times as high as that of commercial Pt/CB. In durability tests, the Pt/Au-G/CB-HT/GC electrode was more stable than commercial Pt/CB electrode. The decrease in electrochemical surface area of Pt for the Pt/Au-G/CB-HT during the initial 2000 cycles was caused by both anodic dissolution of Pt into the electrolyte solution and formation of solid solutions of Pt and Au, while after 2000 cycles it was significantly suppressed.

Pressure Sensitive Essence Microcapsules with MF-UF Resin as Double Wall

The paper studied the preparation and micro-encapsulation of pressure sensitive essence microcapsules with MF resin and UF resin as double wall by using the in situ polymerization method, and the optimal preparation conditions were also studied. The microcapsules were characterized on structure, morphologies, thermal properties, mean particle size and size distribution. The experiment illustrated that the wall of microcapsule consisted of the MF resin and the UF resin had been synthesized in the process of preparation, the essence oil was encapsulated into the microcapsules, the mean particle size and size distribution was well-proportioned and narrowed respectively, the particle morphologies were single core and global, the wall was hermetically sealed.

Spin Polarization and Quantum Spins in Au Nanoparticles

The present study focuses on investigating the magnetic properties and the critical particle size for developing sizable spontaneous magnetic moment of bare Au nanoparticles. Seven sets of bare Au nanoparticle assemblies, with diameters from 3.5 to 17.5 nm, were fabricated with the gas condensation method. Line profiles of the X-ray diffraction peaks were used to determine the mean particle diameters and size distributions of the nanoparticle assemblies. The magnetization curves M(Ha) reveal Langevin field profiles. Magnetic hysteresis was clearly revealed in the low field regime even at 300 K. Contributions to the magnetization from different size particles in the nanoparticle assemblies were considered when analyzing the M(Ha) curves. The results show that the maximum particle moment will appear in 2.4 nm Au particles. A similar result of the maximum saturation magnetization appearing in 2.3 nm Au particles is also concluded through analysis of the dependency of the saturation magnetization MP on particle size. The MP(d) curve departs significantly from the 1/d dependence, but can be described by a log-normal function. Magnetization can be barely detected for Au particles larger than 27 nm. Magnetic field induced Zeeman magnetization from the quantum confined Kubo gap opening appears in Au nanoparticles smaller than 9.5 nm in diameter.

Recoverability of freeze-dried doxorubicin-releasing chitosan embolic microspheres

The purpose of this study is to investigate the recoverability of freeze-dried chitosan microspheres (MS). The factors influencing the integrity of chitosan MS during freeze-drying and rehydration procedures were determined, with focusing on choosing a suitable rehydration method and a freeze-drying excipient. Mean MS size, size distribution and sphericity of recovered chitosan MS were evaluated. Furthermore, the impacts of freeze-drying and rehydration procedure on the elasticity of chitosan MS were explored and the release profiles were evaluated. The recoverability of lyophilized chitosan MS was largely dependent on rehydration method and freeze-drying excipients. When using the optimized recovery processes, deformable drug-loaded chitosan MS can be rapidly recovered to exhibit the initial physico-mechanical properties such as elasticity. Release profiles also were not significantly changed after rehydration procedure. It is therefore expected drug-loaded chitosan MS can be stably freeze-dried with the prevention of drug release during storage and rapidly recovered to be used as deformable embolic materials possibly applicable for anti-cancer embolotherapy.

Silver nanoparticles produced by PLD in vacuum: role of the laser wavelength used

In this work we report the results of investigation of silver (Ag) nanoparticles prepared on a silica substrate by laser ablation. Our attention was focused on the mean diameter, size distribution and optical absorption properties of nanoparticles prepared in vacuum by using different laser wavelengths. The fundamental wavelength and the second, third, and fourth harmonics of a nanosecond Nd:YAG laser were used for nanoparticles fabrication. The corresponding values of the laser fluence for each wavelength were: 0.6 J/cm2 at 266 nm, 0.8 J/cm2 at 355 nm, 2.8 J/cm2 at 532 nm, and 2 J/cm2 at 1064 nm. The Ag nanoparticles produced have mean diameters in the range from 2 nm to 12 nm as the nanoparticles’ size decreases with the decrease of the wavelength used. The presence of the Ag nanoparticles was also evidenced by the appearance of a strong optical absorption band in the measured UV-VIS spectra associated with surface plasmon resonance (SPR). A redshift and widening of the absorption peak were observed as the laser wavelength was increased. Some additional investigations were performed in order to clarify the structure of the Ag nanoparticles.

Hydrolysis of insoluble cellulose to glucose catalyzed by cellulase‐containing liposomes in an aqueous solution of 1‐butyl‐3‐methylimidazolium chloride

The liposome containing cellulase from Trichoderma viride was prepared under the condition that an appreciable amount of cellulase was incorporated in lipid membranes. The liposomal cellulase and free enzyme were examined in their hydrolytic activities to insoluble cellulose powder CC31 in the acetate buffer solution (pH 4.8) of 15 w/w% [Bmim][Cl] (1-butyl-3-methylimidazolium chloride). The mean diameter and size distribution of cellulase-containing liposome were practically unchanged under the above condition. The free cellulase was deactivated more rapidly than the liposomal cellulase in catalyzing the hydrolysis of 2.0 g/l CC31 at 45°C in the presence of [Bmim][Cl] for 48 h. The activities of liposomal and free cellulase to cellobiose as soluble substrate were less susceptible to [Bmim][Cl] than their cellulolytic activities to CC31, meaning that β-glucosidase is relatively stable among the three enzyme components of cellulase. The rate of glucose production could be appreciably improved by the pretreatment of CC31 with [Bmim][Cl] alone at 120°C for 30 min followed by the liposomal cellulase-catalyzed hydrolysis of the substrate at 45°C at the [Bmim][Cl] concentration of 15 w/w%.

Measurement of Magnetic Properties Relevant to Heat-Assisted-Magnetic-Recording

Heat-assisted magnetic recording (HAMR) is likely the successor of perpendicular magnetic recording (PMR) technology. The quality of HAMR writing is dominated not by the magnetic field gradient (as in PMR), but by the high thermal gradient generated by the laser heating spot. Knowledge of temperature dependence of magnetic parameters: anisotropy field Hk(T), saturation moment Ms(T) and anisotropy field distribution (δHk) the proximity of Curie temperature is crucial for media development. Here we describe a new system to probe the magnetic properties close to Tc, as well as a semianalytical model to explain the results. The model takes into account the thermal fluctuations; input into the model are experimentally measured data for Ms(T), Hk(T), mean field demagnetization factor, σHk and grain size distribution. In the paper we present two types of data: 1) thermal erasure in the absence of a magnetic field; and 2) thermomagnetic writing, allowing the estimate of the switching field distribution at high temperatures.

Fluorescence enhancement effect in pyrene and perylene doped nanoporous polystyrene films: Mechanistic and morphology

AbstractLuminescent porous polystyrene (PS) films containing pyrene and various amounts of perylene were prepared in humid atmosphere by solution casting technique for use as a plastic scintillator. The fluorescence spectra of doped PS films monitored at pyrene excitation show quenching of monomer fluorescence of pyrene with simultaneous sensitization of perylene monomer fluorescence appearing towards red. The observed enhancement in fluorescence of perylene was explained by considering excitation energy transfer (EET) from pyrene to perylene molecules accommodated in the pores generated during film formation. The fluorescence quenching data do not fit into the Stern–Volmer relation, but the sensitized fluorescence is fitted by an exponential growth equation, y = 201 860 433.29 ex/0.64366 + 0.49262, with correlation coefficient R2 = 0.997. The results on absorption and excitation spectroscopy indicated that the pyrene and perylene filled in pores of the PS films exist as isolated molecules. The porosity of the films was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), showing randomly oriented holes, and their mean size and size distribution were found to be depending upon the dopant concentration.Pyrene and perylene doped porous PS films prepared by solution casting method in humid atmosphere showed highly intense blue perylene fluorescence by fluorescence resonance energy transfer (FRET) at pyrene excitation. The SEM and AFM images revealed that nanosized pores are perylene concentration dependent, both pyrene and perylene held in the cavity of the pores in close proximal distance less than 10 nm is required to cause efficient energy transfer between them.

Size-dependent photoluminescence in silicon nanostructures: quantum confinement effect

Visible photoluminescence (PL) from laser-etched silicon nanostructures has been analysed. A systematic size dependence study of PL from silicon nanostructures has been performed. The PL from these structures is attributed to the quantum confinement effect. Different quantum confinement models have been used for PL and Raman lineshape fitting to calculate the mean size and size distribution of silicon nanostructures and the results are comparatively studied. Calculated values of oscillator strength and radiative lifetime show that PL is due to radiative recombination of confined excitons.

Radiation synthesis of nanosilver/poly vinyl alcohol/cellulose acetate/gelatin hydrogels for wound dressing

Ag nanoparticles (AgNPs) supported within polyvinyl alcohol/cellulose acetate/gelatin (PVA/CA/GEL) composite have been successfully synthesized using gamma radiation-induced crosslinking as novel in situ method. The reduction of Ag+ ions within the previously obtained hydrogel matrix was performed using further radiation. The successful incorporation of silver nanoparticles in PVA/CA/GEL matrix was confirmed by UV–Vis spectroscopy, X-ray diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray (EDX) analysis and Fourier transform infrared (FTIR) spectroscopy. It was found that PVA/CA/GEL-stabilized silver nanocomposite hydrogel revealed the presence of well-dispersed and spherical silver nanoparticles, the mean diameter and size distribution of nanoparticles increased with enhanced loaded AgNO3 concentration. The mean diameters of 5, 10 and 20 mM AgNO3 loaded PVA/CA/GEL were 38.6 nm, 56.8 nm and 60.1 nm whereas, 25 % of size distribution was < 37.0 nm, < 60.7 nm and < 63.0 nm, respectively. The mechanical properties of the membranes were characterized by tensile tests; the hydrogel membrane had sufficient strength. TGA showed a higher thermal stability for Ag/PVA/CA/GEL nanocomposite than the conventional ones. XRD results indicated that Ag-nano particle inhibit the crystallization of PVA-based gel and presence of silver nano-particle in the hydrogel nanocomposite. The nanosilver/PVA/CA/GEL hydrogels were found to have antimicrobial activity against various fungus and bacteria. The antibacterial ability could be significantly enhanced by the increasing of AgNO3 content. In vitro bacterial adhesion study indicated a significant difference between neat and nanocomposite gel which showed higher inhibition. It suggested that the nanosilver hydrogels could be tried as wound dressing.